The present invention relates to manganese (III)-containing nickel(II) hydroxide, a process for its production and its use as electrode material for secondary batteries.
Nickel(II) hydroxide is used in the alkaline accumulator as positive electrode mass. Changes in certain electrochemical properties are produced by incorporating various extraneous ions.
The incorporation of manganese ions in nickel(II) hydroxide is described in only a few publications. A reason for this is that the bivalent manganese in .beta.-Mn(OH).sub.2 or in the mixed oxide with nickel is already very easily oxidized by atmospheric oxygen and the manganese in the end product does not exist in a defined oxidation state. The preparation of uniform products is thereby complicated.
Some references on the properties of manganese-doped nickel hydroxide electrodes are known from the literature:
J. P. Harivel, B. Morignat, J. Labat, J. F. Laurent, Power Sources 1966, Pergamon Press, ed. by D. H. Collins, p. 239, doped nickel(II) hydroxide with Mn.sup.2+ or Mn.sup.4+ by co-precipitation from aqueous sodium hydroxide solution. The doped hydroxides showed no improvements in the electrochemical properties by comparison with pure nickel hydroxide.
Cordoba et al. investigated the effect of nickel hydroxides doped with manganese and/or iron on the application as oxygen electrodes (S.I. Cordoba, M. Lopez Teijelo, V. A. Macagno, Electrochimica Acta 32 (1987), 1783, S. I. Cordoba, R. E. Carbonio, M. Lopez Teijelo, V. A. Macagno, Electrochimica Acta 31 (1986), 1321). The materials were here produced likewise by coprecipitation or else by deposition of the pure hydroxides above each other in layers.
D. A. Corrigan, R. M. Bendert, J. Electrochem. Soc. 136 (1989), 723 and D. Belanger, G. Laperriere, J. Electrochem. Soc. 137 (1990), 2355 carried out cyclovoltammetric studies on cathodically deposited thin layers of Mn.sup.2+ -doped nickel hydroxide among other systems.
Practical conclusions with regard to the improvement of the properties and/or application of these materials in secondary batteries cannot, however, be derived from the literature mentioned.
The manganese-doped nickel hydroxide materials known from the prior art, as have been used up to now for the production of electrodes for secondary batteries, therefore have no important advantage over undoped material.
It was now the object of the invention so to improve the properties of manganese-doped nickel hydroxide powder for the production of battery electrodes that the capacity of the nickel hydroxide electrodes would be raised and the cyclic stability simultaneously improved.